Self-cleaning ink jet printer with oscillating septum and method of assembling the printer

ABSTRACT

Self-cleaning printer with reverse fluid flow and method of assembling the printer. The printer comprises a print head defining a plurality of ink channels therein, each ink channel terminating in an ink ejection orifice. The print head also has a surface thereon surrounding all the orifices. Contaminant may reside on the surface and also may completely or partially obstruct the orifice. Therefore, a cleaning assembly is disposed relative to the surface and/or orifice for directing a flow of fluid along the surface and/or across the orifice to clean the contaminant from the surface and/or orifice. The cleaning assembly includes an oscillatable septum disposed opposite the surface or orifice for defining a gap therebetween. Presence of the oscillatable septum accelerates the flow of fluid through the gap to induce a hydrodynamic shearing force in the fluid. This shearing force acts against the contaminant to clean the contaminant from the surface and/or orifice. A pump in fluid communication with the gap is also provided for pumping the fluid through the gap. As the surface and/or orifice is cleaned, the contaminant is entrained in the fluid. A filter is provided to separate the contaminant from the fluid.

BACKGROUND OF THE INVENTION

This invention generally relates to ink jet printer apparatus andmethods and more particularly relates to a self-cleaning ink jet printerwith oscillating septum and method of assembling the printer.

An ink jet printer produces images on a receiver by ejecting inkdroplets onto the receiver in an imagewise fashion. The advantages ofnon-impact, low-noise, low energy use, and low cost operation inaddition to the capability of the printer to print on plain paper arelargely responsible for the wide acceptance of ink jet printers in themarketplace.

In this regard, “continuous” ink jet printers utilize electrostaticcharging tunnels that are placed close to the point where ink dropletsare being ejected in the form of a stream. Selected ones of the dropletsare electrically charged by the charging tunnels. The charged dropletsare deflected downstream by the presence of deflector plates that have apredetermined electric potential difference between them. A gutter maybe used to intercept the charged droplets, while the uncharged dropletsare free to strike the recording medium.

In the case of “on demand” ink jet printers, at every orifice apressurization actuator is used to produce the ink jet droplet. In thisregard, either one of two types of actuators may be used. These twotypes of actuators are heat actuators and piezoelectric actuators. Withrespect to heat actuators, a heater placed at a convenient locationheats the ink and a quantity of the ink will phase change into a gaseoussteam bubble and raise the internal ink pressure sufficiently for an inkdroplet to be expelled to the recording medium. With respect topiezoelectric actuators. A piezoelectric material is used, whichpiezoelectric material possess piezoelectric properties such that anelectric field is produced when a mechanical stress is applied. Theconverse also holds true; that is, an applied electric field willproduce a mechanical stress in the material. Some naturally occurringmaterials possessing these characteristics are quartz and tourmaline.The most commonly produced piezoelectric ceramics are lead zirconatetitanate, barium titanate, lead titanate, and lead metaniobate.

Inks for high speed ink jet printers, whether of the “continuous” or“piezoelectric” type, must have a number of special characteristics. Forexample, the ink should incorporate a nondrying characteristic, so thatdrying of ink in the ink ejection chamber is hindered or slowed to sucha state that by occasional spitting of ink droplets, the cavities andcorresponding orifices are kept open. The addition of glycol facilitatesfree flow of ink through the ink jet chamber. Of course, the ink jetprint head is exposed to the environment where the ink jet printingoccurs. Thus, the previously mentioned orifices are exposed to manykinds of air born particulates. Particulate debris may accumulate onsurfaces formed around the orifices and may accumulate in the orificesand chambers themselves. That is, the ink may combine with suchparticulate debris to form an interference burr that blocks the orificeor that alters surface wetting to inhibit proper formation of the inkdroplet. The particulate debris should be cleaned from the surface andorifice to restore proper droplet formation. In the prior art, thiscleaning is commonly accomplished by brushing, wiping, spraying, vacuumsuction, and/or spitting of ink through the orifice.

Thus, inks used in ink jet printers can be said to have the followingproblems: the inks tend to dry-out in and around the orifices resultingin clogging of the orifices; and the wiping of the orifice plate causeswear on plate and wiper, the wiper itself producing particles that clogthe orifice.

Ink jet print head cleaners are known. An ink jet print head cleaner isdisclosed in U.S. Pat. No. 4,970,535 titled “Ink Jet Print Head FaceCleaner” issued Nov. 13, 1990, in the name of James C. Oswald. Thispatent discloses an in jet print head face cleaner that provides acontrolled air passageway through an enclosure formed against the printhead face. Air is directed through an inlet into a cavity in theenclosure. The air that enters the cavity is directed past ink jetapertures on the head face and then out an outlet. A vacuum source isattached to the outlet to create a subatmospheric pressure in thecavity. A collection chamber and removable drawer are positioned belowthe outlet to facilitate disposal of removed ink. Although the Oswaldpatent does not disclose use of brushes or wipers, the Oswald patentalso does not reference use of a liquid solvent to remove the ink;rather, the Oswald technique uses heated air to remove the ink. However,use of heated air is less effective for cleaning than use of a liquidsolvent. Also, use of heated air may damage fragile electronic circuitrythat may be present on the print head face. Moreover, the Oswald patentdoes not appear to disclose “to-and-fro” movement of air streams orliquid solvent across the head face, which to-and-fro movement mightotherwise enhance cleaning effectiveness.

Therefore, there is a need to provide a self-cleaning printer withoscillating septum and method of assembling the printer.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a self-cleaning printerwith oscillating septum and method of assembling the printer, whichoscillating septum enhances cleaning effectiveness.

With the above object in view, the present invention resides in aself-cleaning printer, comprising a print head having a surface thereon;and an ocsillatable structural member disposed opposite the surface fordefining a gap therebetween sized to allow a flow of fluid in a firstdirection through the gap, said member accelerating the flow of fluid toinduce a shearing force in the flow of fluid while the memberoscillates, whereby the shearing force acts against the surface whilethe shearing force is induced in the flow of fluid and whereby thesurface is cleaned while the shearing force acts against the surface.

According to an exemplary embodiment of the present invention, theself-cleaning printer comprises a print head defining a plurality of inkchannels therein, each ink channel terminating in an orifice. The printhead also has a surface thereon surrounding all the orifices. The printhead is capable of ejecting ink droplets through the orifice, which inkdroplets are intercepted by a receiver (e.g., paper or transparency)supported by a platen roller disposed adjacent the print head.Contaminant such as an oily film-like deposit or particulate matter mayreside on the surface and may completely or partially obstruct theorifice. The oily film may, for example, be grease and the particulatematter may be particles of dirt, dust, metal and/or encrustations ofdried ink. Presence of the contaminant interferes with proper ejectionof the ink droplets from their respective orifices and therefore maygive rise to undesirable image artifacts, such as banding. It istherefore desirable to clean the contaminant from the surface.

Therefore, a cleaning assembly is disposed relative to the surfaceand/or orifice for directing a flow of fluid along the surface and/oracross the orifice to clean the contaminant from the surface and/ororifice. The cleaning assembly includes an oscillating septum disposedopposite the surface and/or orifice for defining a gap therebetween. Thegap is sized to allow the flow of fluid through the gap. Presence of theoscillating septum accelerates the flow of fluid in the gap to induce ahydrodynamic shearing force in the fluid. This shearing force actsagainst the particulate matter and cleans the particulate matter fromthe surface and/or orifice. A pump in fluid communication with the gapis also provided for pumping the fluid through the gap. In addition, afilter is provided to filter the particulate mater from the fluid forlater disposal.

A feature of the present invention is the provision of an oscillatingseptum disposed opposite the surface and/or orifice for defining a gaptherebetween capable of inducing a hydrodynamic shearing force in thegap, which shearing force removes the particulate matter from thesurface and/or orifice.

Another feature of the present invention is the provision of a pipingcircuit for directing fluid flow through the gap.

An advantage of the present invention is that the cleaning assemblybelonging to the invention cleans the contaminant from the surfaceand/or orifice without use of brushes or wipers which might otherwisedamage the surface and/or orifice.

These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there are shown and described illustrativeembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed the invention will be better understood from the followingdetailed description when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a view in elevation of a self-cleaning ink jet printerbelonging to the present invention, the printer including a page-widthprint head;

FIG. 2 is a fragmentation view in vertical section of the print head,the print head defining a plurality of channels therein, each channelterminating in an orifice;

FIG. 3 is a fragmentation view in vertical section of the print head,this view show some of the orifices encrusted with contaminant to beremoved;

FIG. 4 is a view in elevation of a cleaning assembly for removing thecontaminant;

FIG. 5 is a view in vertical section of the cleaning assembly, thecleaning assembly including an oscillating septum disposed opposite theorifice so as to define a gap between the orifice and the septum;

FIG. 6 is an enlarged fragmentation view in vertical section of theoscillating septum;

FIG. 7 is an enlarged fragmentation view in vertical section of thecleaning assembly, this view showing the gap having reduced height dueto increased length of the oscillating septum, for cleaning contaminantfrom within the ink channel;

FIG. 8 is an enlarged fragmentation view in vertical section of thecleaning assembly, this view showing the gap having increased width dueto increased width of the oscillating septum, for cleaning contaminantfrom within the ink channel;

FIG. 9 is a view in vertical section of a second embodiment of theinvention, wherein the cleaning assembly includes a pressurized gassupply in fluid communication with the gap for introducing gas bubblesinto the liquid in the gap; and

FIG. 10 is an enlarged fragmentation view in vertical section of thesecond embodiment of the invention;

FIG. 11 is a view in vertical section of a third embodiment of theinvention, wherein the cleaning assembly includes a pressure pulsegenerator in communication with the gap for generating a plurality ofpressure pulses in the liquid in the gap;

FIG. 12 is a view in vertical section of a fourth embodiment of theinvention, wherein the cleaning assembly includes an expandable septum;

FIG. 13 is an enlarged fragmentation view in vertical section ofexpandable septum; and

FIG. 14 view in vertical section of a fifth embodiment of the invention,wherein the septum is metallic and capable of moving under influence ofa magnetic field established by electromagnets.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown or described may take various forms wellknown to those skilled in the art.

Therefore, referring to FIG. 1, there is shown a self-cleaning printer,generally referred to as 10, for printing an image 20 on a receiver 30,which may be a reflective-type receiver (e.g., paper) or atransmissive-type receiver (e.g., transparency). Receiver 30 issupported on a platen roller 40 which is capable of being rotated by aplaten roller motor 50 engaging platen roller 40. Thus, when platenroller motor 50 rotates platen roller 40, receiver 30 will advance in adirection illustrated by a first arrow 55.

Referring to FIGS. 1 and 2, printer 10 also comprises a “page-width”print head 60 disposed adjacent to platen roller 40. Print head 60comprises a print head body 65 having a plurality of ink channels 70,each channel 70 terminating in a channel outlet 75. In addition, eachchannel 70, which is adapted to hold an ink body 77 therein, is definedby a pair of oppositely disposed parallel side walls 79 a and 79 b.Attached, such as by a suitable adhesive, to print head body 65 is acover plate 80 having a plurality of orifices 85 formed therethroughcolinearly aligned with respective ones of channel outlets 75. A surface90 of cover plate 80 surrounds all orifices 85 and faces receiver 20. Ofcourse, in order to print image 20 on receiver 30, an ink droplet 100must be released from orifice 85 in direction of receiver 20, so thatdroplet 100 is intercepted by receiver 20. To achieve this result, printhead body 65 may be a “piezoelectric ink jet” print head body formed ofa piezoelectric material, such as lead zirconium titanate (PZT). Such apiezoelectric material is mechanically responsive to electrical stimuliso that side walls 79 a/b simultaneously inwardly deform whenelectrically stimulated. When side walls 79 a/b simultaneously inwardlydeform, volume of channel 70 decreases to squeeze ink droplet 100 fromchannel 70. Ink droplet 100 is preferably ejected along a first axis 107normal to orifice 85. Of course, ink is supplied to channels 70 from anink supply container 109. Also, supply container 109 is preferablypressurized such that ink pressure delivered to print head 60 iscontrolled by an ink pressure regulator 110.

Still referring to FIGS. 1 and 2, receiver 30 is moved relative topage-width print head 60 by rotation of platen roller 40, which iselectronically controlled by paper transport control system 120. Papertransport control system 120 is in turn controlled by controller 130.Paper transport control system 120 disclosed herein is by way of exampleonly, and many different configurations are possible based on theteachings herein. In the case of page-width print head 60, it is moreconvenient to move receiver 30 past stationary head 60. Controller 130,which is connected to platen roller motor 50, ink pressure regulator 110and a cleaning assembly, enables the printing and print head cleaningoperations. Structure and operation of the cleaning assembly isdescribed in detail hereinbelow. Controller 130 may be a modelCompuMotor controller available from Parker Hannifin in Rohrnert Park,Calif.

Turning now to FIG. 3, it has been observed that cover plate 80 maybecome fouled by contaminant 140. Contaminant 140 may be, for example,an oily film or particulate matter residing on surface 90. Contaminant140 also may partially or completely obstruct orifice 85. Theparticulate matter may be, for example, particles of dirt, dust, metaland/or encrustations of dried ink. The oily film may be, for example,grease or the like. Presence of contaminant 140 is undesirable becausewhen contaminant 140 completely obstructs orifice 85, ink droplet 100 isprevented from being ejected from orifice 85. Also, when contaminant 140partially obstructs orifice 85, flight of ink droplet 100 may bediverted from first axis 107 to travel along a second axis 145 (asshown). If ink droplet 100 travels along second axis 145, ink droplet100 will land on receiver 30 in an unintended location. In this manner,such complete or partial obstruction of orifice 85 leads to printingartifacts such as “banding”, a highly undesirable result. Also, presenceof contaminant 140 may alter surface wetting and inhibit properformation of droplet 100. Therefore, it is desirable to clean (i.e.,remove) contaminant 140 to avoid printing artifacts.

Therefore, referring to FIGS. 1, 4, 5 and 6, a cleaning assembly,generally referred to as 170, is disposed proximate surface 90 fordirecting a flow of cleaning liquid along surface 90 and across orifice85 to clean contaminant 140 therefrom. Cleaning assembly 170 is movablefrom a first or “rest” position 172 a spaced-apart from surface 90 to asecond position 172 b engaging surface 90. This movement is accomplishedby means of an elevator 175 coupled to controller 130. Cleaning assembly170 may comprise a housing 180 for reasons described presently. Disposedin housing 180 is a generally rectangular cup 190 having an open end195. Cup 190 defines a cavity 197 communicating with open end 195.Attached, such as by a suitable adhesive, to open end 195 is anelastomeric seal 200, which may be rubber or the like, sized to encircleone or more orifices 85 and sealingly engage surface 90. Extending alongcavity 197 and oriented perpendicularly opposite orifices 85 is astructural member, such as an elongate oscillatable septum 210. Forreasons provided momentarily, septum 210 is preferably made of apiezoelectric material, such as lead zirconate titanate (PZT). In thisregard a mechanical stress is produced in the material when an appliedelectric field is applied. This mechanical stress will bend (i.e.,deform) the material in a preferred direction depending on the directionin which the piezoelectric material is “polled”. Septum 210 has an endportion 215 which, when disposed opposite orifice 85, defines a gap 220of predetermined size between orifice 85 and end portion 215. Moreover,end portion 215 of septum 210 may be disposed opposite a portion ofsurface 90, not including orifice 85, so that gap 220 is defined betweensurface 90 and end portion 215. As described in more detail hereinbelow,gap 220 is sized to allow flow of a liquid therethrough in order toclean contaminant 140 from surface 90 and/or orifice 85. In addition,coupled to septum 210 near end portion 215 are a pair of transducers 218a and 218 b for inducing an electric field in end portion 215. In thepreferred embodiment of the invention, transducers 218 a/b are metalplates capable of conducting electricity, thereby generating theelectric field. Thus, to generate the electric field, transducers 218a/b are connected to a suitable power source (not shown). When theelectric field is induced in end portion 215, the end portion 215 willbend in a preferred direction (as shown). Although two transducers 218a/b are preferred, there may be only one transducer, if desired. In anyevent, when two transducers 218 a/b are used, the transducers 218 a/bare enabled sequentially (i.e., alternately). That is, when transducer218 a is enabled, transducer 218 b is not enabled. Conversely, whentransducer 218 b is enabled, transducer 218 a is not enabled. In thismanner, the sequentially enabling transducers 218 a/b causes aoscillatory “to-and-fro motion” of the liquid in gap 200. Thisto-and-fro motion of the liquid in turn causes a “sweeping” action whichhas been found to increase cleaning effectiveness. By way of exampleonly, not by way of limitation, the frequency of the to-and-fro motionmay be between approximately 1 Hz and 5 MHz. Also, by way of exampleonly, and not by way of limitation, the velocity of the liquid flowingthrough gap 220 may be about 1 to 20 meters per second. Further by wayof example only, and not by way of limitation, height of gap 220 may beapproximately 3 to 30 thousandths of an inch. Moreover, hydrodynamicpressure applied to contaminant 140 in gap 220 due, at least in part, topresence of septum 210 may be approximately 1 to 30 psi (pounds persquare inch). Septum 210 partitions (i.e., divides) cavity 197 into anfirst chamber 230 and a second chamber 240, for reasons described morefully hereinbelow.

Referring to FIG. 5, interconnecting first chamber 230 and secondchamber 240 is a closed-loop piping circuit 250. It will be appreciatedthat piping circuit 250 is in fluid communication with gap 220 forrecycling the liquid through gap 220. In this regard, piping circuit 250comprises a first piping segment 260 extending from second chamber 240to a reservoir 270 containing a supply of the liquid. Piping circuit 250further comprises a second piping segment 280 extending from reservoir270 to first chamber 230. Disposed in second piping segment 280 is arecirculation pump 290. Pump 290 pumps the liquid from reservoir 270,through second piping segment 280, into first chamber 230, through gap220, into second chamber 240, through first piping segment 260 and backto reservoir 270, as illustrated by a plurality of second arrows 295.Disposed in first piping segment 260 may be a first filter 300 anddisposed in second piping segment 280 may be a second filter 310 forfiltering (i.e., separating) contaminant 140 from the liquid as theliquid circulates through piping circuit 250. It will be appreciatedthat portions of the piping circuit 250 adjacent to cup 190 arepreferably made of flexible tubing in order to facilitate uninhibitedtranslation of cup 190 toward and away from print head 60, whichtranslation is accomplished by means of elevator 175.

Referring again to FIG. 5, a first valve 320 is preferably disposed at apredetermined location in first piping segment 260, which first valve320 is operable to block flow of the liquid through first piping segment260. Also, a second valve 330 is preferably disposed at a predeterminedlocation in second piping segment 280, which second valve 330 isoperable to block flow of the liquid through second piping segment 280.In this regard, first valve 320 and second valve 330 are located infirst piping segment 260 and second piping segment 280, respectively, soas to isolate cavity 197 from reservoir 270, for reasons describedmomentarily. A third piping segment 340 has an open end thereofconnected to first piping segment 260 and another open end thereofreceived into a sump 350. In communication with sump 350 is a suction(i.e., vacuum) pump 360 for reasons described presently. Suction pump360 drains cup 190 and associated piping of cleaning liquid before cupis detached and returned to first position 172 a. Moreover, disposed inthird piping segment 340 is a third valve 370 operable to isolate pipingcircuit 250 from sump 350.

Referring to FIGS. 5 and 6, during operation of cleaning assembly 170,first valve 320 and second valve 310 are opened while third valve 370 isclosed. Recirculation pump 290 is then operated to draw the liquid fromreservoir 270 and into first chamber 230. The liquid will then flowthrough gap 220. However, as the liquid flows through gap 220, ahydrodynamic shearing force will be induced in the liquid due topresence of end portion 215 of septum 210. It is believed this shearingforce is in turn caused by a hydrodynamic stress forming in the liquid,which stress has a “normal” component δ_(n) acting normal to surface 90(or orifice 85) and a “shear” component τ acting along surface 90 (oracross orifice 85). Vectors representing the normal stress componentδ_(n) and the shear stress components τ are best seen in FIG. 6. Thepreviously mentioned hydrodynamic shearing force acts on contaminant 140to remove contaminant 140 from surface 90 and/or orifice 85, so thatcontaminant 140 becomes entrained in the liquid flowing through gap 220.In addition, transducers 218 a and 218 b are alternately enabled toproduce the previously mentioned “sweeping” motion of end portion 215 ofseptum 210. This sweeping motion in turn causes the liquid in gap 220 tomove back-and-forth to further loosen contaminant 140. In this manner,cleaning effectiveness is enhanced. As contaminant 140 is cleaned fromsurface 90 and orifice 85, the liquid with contaminant 140 entrainedtherein, flows into second chamber 240 and from there into first pipingsegment 260. As recirculation pump 290 continues to operate, the liquidwith entrained contaminant 140 flows to reservoir 270 from where theliquid is pumped into second piping segment 280. However, it ispreferable to remove contaminant 140 from the liquid as the liquid isrecirculated through piping circuit 250. This is preferred in order thatcontaminant 140 is not redeposited onto surface 90 and across orifice85. Thus, first filter 300 and second filter 310 are provided forfiltering contaminant 140 from the liquid recirculating through pipingcircuit 250. After a desired amount of contaminant 140 is cleaned fromsurface 90 and/or orifice 85, recirculation pump 290 is caused to ceaseoperation and first valve 320 and second valve 330 are closed to isolatecavity 197 from reservoir 270. At this point, third valve 370 is openedand suction pump 360 is operated to substantially suction the liquidfrom first piping segment 260, second piping segment 280 and cavity 197.This suctioned liquid flows into sump 350 for later disposal. However,the liquid flowing into sump 350 is substantially free of contaminant140 due to presence of filters 300/310 and thus may be recycled intoreservoir 270, if desired.

Referring to FIGS. 7 and 8, it has been discovered that length and widthof elongate septum 210 controls amount of hydrodynamic stress actingagainst surface 90 and orifice 85. This effect is important in order tocontrol severity of cleaning action. Also, it has been discovered that,when end portion 215 of septum 210 is disposed opposite orifice 85,length and width of elongate septum 210 controls amount of penetration(as shown) of the liquid into channel 70. It is believed that control ofpenetration of the liquid into channel 70 is in turn a function of theamount of normal stress δ_(n). However, it has been discovered that theamount of normal stress δ_(n) is inversely proportional to height of gap220. Therefore, normal stress δ_(n), and thus amount of penetration ofthe liquid into channel 70, can be increased by increasing length ofseptum 210. Moreover, it has been discovered that amount of normalstress δ_(n) is directly proportional to pressure drop in the liquid asthe liquid slides along end portion 215 and surface 90. Therefore,normal stress δ_(n), and thus amount of penetration of the liquid intochannel 70, can be increased by increasing width of septum 210. Theseeffects are important in order to clean any contaminant 140 which may beadhering to either of side walls 79 a or 79 b. More specifically, whenelongate septum 210 is fabricated so that it has a greater than nominallength X, height of gap 220 is decreased to enhance the cleaning action,if desired. Also, when elongate septum 210 is fabricated so that it hasa greater than nominal width W, the run of gap 220 is increased toenhance the cleaning action, if desired. Thus, a person of ordinaryskill in the art may, without undue experimentation, vary both thelength X and width W of septum 210 to obtain an optimum gap size forobtaining optimum cleaning depending on the amount and severity ofcontaminant encrustation. It may be appreciated from the discussionhereinabove, that a height H of seal 200 also may be varied to vary sizeof gap 220 with similar results.

Returning to FIG. 1, elevator 175 may be connected to cleaning cup 190for elevating cup 190 so that seal 200 sealingly engages surface 90 whenprint head 60 is at second position 172 b. To accomplish this result,elevator 175 is connected to controller 130, so that operation ofelevator 175 is controlled by controller 130. Of course, when thecleaning operation is completed, elevator 175 may be lowered so thatseal no longer engages surface 90.

As best seen in FIG. 1, in order to clean the page-width print head 60using cleaning assembly 170, platen roller 40 has to be moved to makeroom for cup 190 to engage print head 60. An electronic signal fromcontroller 130 activates a motorized mechanism (not shown) that movesplaten roller 40 in direction of first double-ended arrow 387 thusmaking room for upward movement of cup 190. Controller 130 also controlselevator 175 for transporting cup 190 from first position 172 a notengaging print head 60 to second position 172 b (shown in phantom)engaging print head 60. When cup 190 engages print head cover plate 80,cleaning assembly 170 circulates liquid through cleaning cup 190 andover print head cover plate 80. When print head 60 is required forprinting, cup 190 is retracted into housing 180 by elevator 175 to itsresting first position 172 a. The cup 190 may be advanced outwardly fromand retracted inwardly into housing 180 in direction of seconddouble-ended arrow 388.

Still referring to FIG. 1, the liquid emerging from outlet chamber 240initially will be contaminated with contaminant 140. It is desirable tocollect this liquid in sump 350 rather than to recirculate the liquid.Therefore, this contaminated liquid is directed to sump 350 by closingsecond valve 330 and opening third valve 370 while suction pump 360operates. The liquid will then be free of contaminant 140 and may berecirculated by closing third valve 370 and opening second valve 330. Adetector 397 is disposed in first piping segment 260 to determine whenthe liquid is clean enough to be recirculated. Information from detector397 can be processed and used to activate the valves in order to directexiting liquid either into sump 350 or into recirculation. In thisregard, detector 397 may be a spectrophotometric detector. In any event,at the end of the cleaning procedure, suction pump 360 is activated andthird valve 370 is opened to suction into sump 350 any trapped liquidremaining between second valve 330 and first valve 320. This processprevents spillage of liquid when cleaning assembly 170 is detached fromcover plate 80. Further, this process causes cover plate 80 to besubstantially dry, thereby permitting print head 60 to function withoutimpedance from cleaning liquid drops being around orifices 85. To resumeprinting, sixth valve 430 is closed and fifth valve 420 is opened toprime channel 70 with ink. Suction pump 360 is again activated, andthird valve 370 is opened to suction any liquid remaining in cup 190.Alternatively, the cup 190 may be detached and a separate spittoon (notshown) may be brought into alignment with print head 60 to collect dropsof ink that are ejected from channel 70 during priming of print head 60.

The mechanical arrangement described above is but one example. Manydifferent configurations are possible. For example, print head 60 may berotated outwardly about a horizontal axis 389 to a convenient positionto provide clearance for cup 190 to engage print head cover plate 80.

Referring to FIGS. 9 and 10, there is shown a second embodiment of thepresent invention. In this second embodiment of the invention, apressurized gas supply 390 is in communication with gap 220 forinjecting a pressurized gas into gap 220. The gas will form amultiplicity of gas bubbles 395 in the liquid to enhance cleaning ofcontaminant 140 from surface 90 and/or orifice 85.

Referring to FIG. 11, there is shown a third embodiment of the presentinvention. In this third embodiment of the invention, a pressure pulsegenerator, such as a piston arrangement, generally referred to as 400,is in fluid communication with first chamber 230. Piston arrangement 400comprises a reciprocating piston 410 for generating a plurality ofpressure pulse waves in first chamber 230, which pressure wavespropagate in the liquid in first chamber 230 and enter gap 220. Piston410 reciprocates between a first position and a second position, thesecond position being shown in phantom. The effect of the pressure wavesis to enhance cleaning of contaminant 140 from surface 90 and/or orifice85 by force of the pressure waves.

Referring to FIGS. 12 and 13, there is shown a fourth embodiment of thepresent invention. In this fourth embodiment of the invention, elongateseptum 210 has a bore 420 longitudinally therein. In this septum 210 ispreferably made of an elastomeric piezoelectric material, such as arubber and PZT composition. Coupled to bore 420 is a pneumatic pump 430for pumping a gas (e.g., air) into bore 420. As the gas is pumped intobore 420, elastic septum 210 is pressurized so that septum 210 expandsto greater width W and greater length X to obtain the enhanced cleaningeffect described hereinabove. In this manner, septum 210 is expandablefrom a first volume thereof to a second volume greater than the firstvolume. Moreover, a bleed valve 440 is preferably provided. Bleed valve440 is closed while pump 430 operates to expand elastic septum 210.After the desired cleaning is achieved, pump 430 is caused to ceaseoperation and bleed valve 440 is opened to release the gas from bore420. As the gas is released from bore 420, septum 210 will return to itsinitial first volume.

Referring to FIG. 14, there is shown a fifth embodiment of the presentinvention. In this fifth embodiment of the invention, septum 210 isformed of a metallic material so that septum 210 is movable underinfluence of a magnetic field. A pair of opposing electromagnets 450 a/bare attached to an inside wall of cavity 197 near end portion 215 ofseptum 210. Magnets 450 a/b are sequentially enabled to sequentiallygenerate an magnetic field acting on end portion 215 of septum 210. Aseach magnet 450 a or 450 b is enabled, end portion 215 will be drawn tothe magnet in order to obtain the previously mentioned “sweeping” motionof end portion 215. Of course, this sweeping motion enhances cleaningeffectiveness, as previously described.

The cleaning liquid may be any suitable liquid solvent composition, suchas water, isopropanol, diethylene glycol, diethylene glycol monobutylether, octane, acids and bases, surfactant solutions and any combinationthereof. Complex liquid compositions may also be used, such asmicroemulsions, micellar surfactant solutions, vesicles and solidparticles dispersed in the liquid.

It may be appreciated from the description hereinabove, that anadvantage of the present invention is that cleaning assembly 170 cleanscontaminant 140 from surface 90 and/or orifice 85 without use of brushesor wipers which might otherwise damage surface 90 and/or orifice 85.This is so because septum 210 induces shear stress in the liquid thatflows through gap 220 to clean contaminant 140 from surface 90 and/ororifice 85.

It may be appreciated from the description hereinabove, that anotheradvantage of the present invention is that cleaning efficiency isincreased. This is so because operation of oscillating transducers 218a/b induce to-and-fro motion of the cleaning fluid in the gap, therebyagitating the liquid coming into contact with contaminant 140. Agitationof the liquid in this manner in turn agitates contaminant 140 in orderto loosen contaminant 140.

While the invention has been described with particular reference to itspreferred embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements of the preferred embodiments without departing from theinvention. In addition, many modifications may be made to adapt aparticular situation and material to a teaching of the present inventionwithout departing from the essential teachings of the invention. Forexample, a heater may be disposed in reservoir 270 to heat the liquidtherein for enhancing cleaning of surface 90, channel 70 and/or orifice85. This is particularly useful when the cleaning liquid is of a typethat increases in cleaning effectiveness as temperature of the liquid isincreased. As another example, in the case of a multiple color printerhaving a plurality of print heads corresponding to respective ones of aplurality of colors, one or more dedicated cleaning assemblies per colormight be used to avoid cross-contamination of print heads by inks ofdifferent colors. As yet another example, a contamination sensor may beconnected to cleaning assembly 170 for detecting when cleaning isneeded. In this regard, such a contamination sensor may a pressuretransducer in fluid communication with ink in channels 70 for detectingrise in ink back pressure when partially or completely blocked channels70 attempt to eject ink droplets 100. Such a contamination sensor mayalso be a flow detector in communication with ink in channels 70 todetect low ink flow when partially or completely blocked channels 70attempt to eject ink droplets 100. Such a contamination sensor may alsobe an optical detector in optical communication with surface 90 andorifices 85 to optically detect presence of contaminant 140 by means ofreflection or emissivity. Such a contamination sensor may also be adevice measuring amount of ink released into a spittoon-like containerduring predetermined periodic purging of channels 70. In this case, theamount of ink released into the spittoon-like container would bemeasured by the device and compared against a known amount of ink thatshould be present in the spittoon-like container if no orifices wereblocked by contaminant 140. Moreover, controller 130 may drive otherauxiliary functions.

Therefore, what is provided is a self-cleaning printer with oscillatingseptum and method of assembling the printer.

PARTS LIST

H . . . height of seal

W . . . greater width of fabricated septum

X . . . greater length of fabricated septum

10 . . . printer

20 . . . image

30 . . . receiver

40 . . . platen roller

50 . . . platen roller motor

55 . . . first arrow

60 . . . print head

65 . . . print head body

70 . . . channel

75 . . . channel outlet

77 . . . ink body

79 a/b . . . side walls

80 . . . cover plate

85 . . . orifice

90 . . . surface

100 . . . ink droplet

107 . . . first axis

109 . . . ink supply container

110 . . . ink pressure regulator

120 . . . paper transport control system

130 . . . controller

140 . . . contaminant

145 . . . second axis

170 . . . cleaning assembly

172 a . . . first position (of cleaning assembly)

172 b . . . second position (of cleaning assembly)

175 . . . elevator

180 . . . housing

190 . . . cup

195 . . . open end (of cup)

197 . . . cavity

200 . . . seal

210 . . . septum

215 . . . end portion (of septum)

218 a/b . . . transducers

220 . . . gap

230 . . . first chamber

240 . . . second chamber

250 . . . piping circuit

260 . . . first piping segment

270 . . . reservoir

280 . . . second piping segment

290 . . . recirculation pump

295 . . . second arrows

300 . . . first filter

310 . . . second filter

320 . . . first valve

330 . . . second valve

340 . . . third piping segment

350 . . . sump

360 . . . suction pump

370 . . . third valve

380 . . . 4-way valve

382 . . . air bleed valve

385 . . . third arrows

387 . . . first double-headed arrow

388 . . . second double-headed arrow

389 . . . horizontal plane

390 . . . gas supply

395 . . . gas bubbles

397 . . . detector

400 . . . piston arrangement

410 . . . piston

420 . . . bore

430 . . . pneumatic pump

440 . . . bleed valve

450 a/b . . . electromagnets

What is claimed is:
 1. A self-cleaning printer, comprising: (a) a printhead having a surface thereon; and (b) an oscillatable structural memberdisposed opposite the surface for defining a gap therebetween sized toallow a flow of fluid in a first direction through the gap, said memberaccelerating the flow of fluid to induce a shearing force in the flow offluid while the member oscillates, whereby the shearing force actsagainst the surface while the shearing force is induced in the flow offluid and whereby the surface is cleaned while the shearing force actsagainst the surface.
 2. The self-cleaning printer of claim 1, furthercomprising a pump in fluid communication with the gap for pumping thefluid through the gap.
 3. The self-cleaning printer of claim 1, furthercomprising a gas supply in fluid communication with the gap forinjecting a gas into the gap to form a gas bubble in the flow of fluidfor enhancing cleaning of the surface.
 4. The self-cleaning printer ofclaim 1, further comprising a pressure pulse generator in fluidcommunication with the gap for generating a pressure wave in the flow offluid to enhance cleaning of the surface.
 5. The self-cleaning printerof claim 1, wherein said structural member is expandable from a firstvolume to a second volume greater than the first volume.
 6. Aself-cleaning printer, comprising: (a) a print head having a surfacesusceptible to having contaminant thereon; and (b) a cleaning assemblydisposed relative to the surface for directing a flow of fluid in afirst direction along the surface to clean the contaminant from thesurface, said assembly including an oscillatable septum disposedopposite the surface for defining a gap therebetween sized to allow theflow of fluid through the gap, said septum oscillating in response to anelectric field for accelerating the flow of fluid to induce ahydrodynamic shearing force in the flow of fluid, whereby the shearingforce acts against the contaminant while the shearing force is inducedin the flow of fluid and whereby the contaminant is cleaned from thesurface while the shearing force acts against the contaminant.
 7. Theself-cleaning printer of claim 6, further comprising a transducerconnected to said septum for generating an electric field to oscillatesaid septum.
 8. The self-cleaning printer of claim 6, further comprisinga pump in fluid communication with the gap for pumping the fluid andcontaminant from the gap.
 9. The self-cleaning printer of claim 6,further comprising a pressurized gas supply in fluid communication withthe gap for injecting a pressurized gas into the gap to form a pluralityof gas bubbles in the flow of fluid for enhancing cleaning of thecontaminant from the surface.
 10. The self-cleaning printer of claim 6,further comprising a piston arrangement in fluid communication with thegap for generating a pressure wave in the flow of fluid to enhancecleaning of the contaminant from the surface.
 11. The self-cleaningprinter of claim 6, wherein said septum is expandable and has a boretherein.
 12. The self-cleaning printer of claim 11, further comprising:(a) a pump coupled to the bore for pumping a gas into the bore, so thatthe septum expands from a first volume thereof to a second volumegreater than the first volume while said pump pumps the gas into thebore; and (b) a bleed valve coupled to the bore for releasing the gasfrom the bore, so that the septum contracts to the first volume whilesaid valve releases the gas from the bore.
 13. The self-cleaning printerof claim 6, wherein said septum is metallic.
 14. The self-cleaningprinter of claim 13, further comprising an electromagnet disposed nearsaid septum for generating a magnetic field acting on said septum forbending said septum.
 15. A self-cleaning printer, comprising: (a) aprint head having a surface defining an orifice therethrough, theorifice susceptible to contaminant obstructing the orifice; (b) acleaning assembly disposed proximate the surface for directing a flow ofliquid along the surface and across the orifice to clean the contaminantfrom the orifice, said assembly including: (i) a cup sealinglysurrounding the orifice, said cup defining a cavity therein; (ii) anelongate oscillatable septum disposed in said cup perpendicularlyopposite the orifice for defining a gap between the orifice and saidseptum, the gap sized to allow the flow of liquid through the gap, saidseptum dividing the cavity into an first chamber and an second chambereach in communication with the gap, said septum accelerating the flow ofliquid to induce a hydrodynamic shearing force in the flow of liquidwhile said septum oscillates, whereby the shearing force acts againstthe contaminant while the shearing force is induced in the flow ofliquid, whereby the contaminant is cleaned from the orifice while theshearing force acts against the contaminant and whereby the contaminantis entrained in the flow of liquid while the contaminant is cleaned fromthe orifice; (iii) a pump in fluid communication with the second chamberfor pumping the liquid and entrained contaminant from the gap and intothe second chamber; and (c) a controller connected to said cleaningassembly and said print head for controlling operation thereof.
 16. Theself-cleaning printer of claim 15, further comprising a pair of opposingtransducers connected to said septum for oscillating said septum. 17.The self-cleaning printer of claim 15, further comprising a pressurizedgas supply in fluid communication with the gap for injecting apressurized gas into the gap to form a multiplicity of gas bubbles inthe flow of liquid for enhancing cleaning of the contaminant from theorifice.
 18. The self-cleaning printer of claim 15, further comprising areciprocating piston in fluid communication with the first chamber forgenerating a plurality of pressure waves in the flow of liquid toenhance cleaning of the contaminant from the orifice.
 19. Theself-cleaning printer of claim 15, wherein said septum is expandable andhas a bore therein.
 20. The self-cleaning printer of claim 19, furthercomprising: (a) a pump coupled to the bore for pumping a gas into thebore, so that the septum expands from a first volume thereof to a secondvolume greater than the first volume as said pump pumps the gas into thebore; and (b) a bleed valve coupled to the bore for releasing the gasfrom the bore, so that the septum contracts to the first volume as saidvalve releases the gas from the bore.
 21. The self-cleaning printer ofclaim 15, wherein said septum is metallic.
 22. The self-cleaning printerof claim 21, further comprising an electromagnet disposed near saidseptum for generating a magnetic field acting on said septum for bendingsaid septum.
 23. The self-cleaning printer of claim 15, furthercomprising a closed-loop piping circuit in fluid communication with thegap for recycling the flow of liquid through the gap.
 24. Theself-cleaning printer of claim 23, wherein said piping circuitcomprises: (a) a first piping segment in fluid communication with thefirst chamber; and (b) a second piping segment connected to said firstpiping segment, said second piping segment in fluid communication withthe second chamber and connected to said pump, whereby said pump pumpsthe flow of liquid and entrained contaminant from the gap, into thesecond chamber, through said second piping segment, through said secondpiping segment, into the first chamber and back into the gap.
 25. Theself-cleaning printer of claim 24, further comprising: (a) a first valveconnected to said first piping segment and operable to block the flow ofliquid through said first piping segment; (b) a second valve connectedto said second piping segment and operable to block the flow of liquidthrough said second piping segment; and (c) a suction pump interposedbetween said first valve and said second valve for suctioning the liquidand entrained contaminant from said first piping segment and said secondpiping segment while said first valve blocks the first piping segmentand while said second valve blocks said second piping segment.
 26. Theself-cleaning printer of claim 25, further comprising a sump connectedto said suction pump for receiving the flow of liquid and contaminantsuctioned by said suction pump.
 27. The self-cleaning printer of claim23, further comprising a filter connected to said piping circuit forfiltering the contaminant from the flow of liquid.
 28. The self-cleaningprinter of claim 15, further comprising an elevator connected to saidcleaning assembly for elevating said cleaning assembly into engagementwith the surface of said print head.
 29. The method of claim 28, whereinsaid elevator is connected to said controller, so that operation of saidelevator is controlled by said controller.
 30. A method of assembling aself-cleaning printer, comprising the step of disposing an oscillatablestructural member opposite a surface of a print head for defining a gaptherebetween sized to allow a flow of fluid through the gap, the memberaccelerating the flow of fluid to induce a shearing force in the flow offluid while the member oscillates, whereby the shearing force actsagainst the surface while the shearing force is induced in the flow offluid and whereby the surface is cleaned while the shearing force actsagainst the surface.
 31. The self-cleaning printer of claim 30, furthercomprising the step of connecting a pair of opposing transducers to saidmember for oscillating said member.
 32. The method of claim 30, furthercomprising the step of disposing a pump in fluid communication with thegap for pumping the fluid through the gap.
 33. The method of claim 30,further comprising the step of disposing a gas supply in fluidcommunication with the gap for injecting a gas into the gap to form agas bubble in the flow of fluid for enhancing cleaning of the surface.34. The method of claim 30, further comprising the step of disposing apressure pulse generator in fluid communication with the gap forgenerating a pressure wave in the flow of fluid to enhance cleaning ofthe surface.
 35. The method of claim 30, wherein the step of disposingan oscillatable structural member comprises the step of disposing anoscillatable structural member that is expandable from a first volume toa second volume greater than the first volume.
 36. A method ofassembling a self-cleaning printer, comprising the step of disposing acleaning assembly relative to a surface of a print head for directing aflow of fluid along the surface to clean a contaminant from the surface,the assembly including an oscillatable septum disposed opposite thesurface for defining a gap therebetween sized to allow the flow of fluidthrough the gap, the septum oscillating in response to an electric fieldfor accelerating the flow of fluid to induce a hydrodynamic shearingforce in the flow of fluid, whereby the shearing force acts against thecontaminant while the shearing force is induced in the flow of fluid andwhereby the contaminant is cleaned from the surface while the shearingforce acts against the contaminant.
 37. The method of claim 36, furthercomprising the step of connecting a pair of opposing transducers to theseptum for oscillating the septum.
 38. The method of claim 36, furthercomprising the step of disposing a pump in fluid communication with thegap for pumping the fluid and contaminant from the gap.
 39. The methodof claim 36, further comprising the step of disposing a pressurized gassupply in fluid communication with the gap for injecting a pressurizedgas into the gap to form a plurality of gas bubbles in the flow of fluidfor enhancing cleaning of the contaminant from the surface.
 40. Themethod of claim 36, further comprising the step of disposing a pistonarrangement in fluid communication with the gap for generating apressure wave in the flow of fluid to enhance cleaning of thecontaminant from the surface.
 41. The method of claim 36, wherein thestep of disposing a cleaning assembly including an oscillatable septumcomprises the step of disposing a cleaning assembly including anexpandable oscillatable septum having a bore therein.
 42. The method ofclaim 41, further comprising the steps of: (a) coupling a pump to thebore for pumping a gas into the bore, so that the septum expands from afirst volume thereof to a second volume greater than the first volumewhile the pump pumps the gas into the bore; and (b) coupling a bleedvalve to the bore for releasing the gas from the bore, so that theseptum contracts to the first volume while the valve releases the gasfrom the bore.
 43. The method of claim 36, wherein the step of disposinga cleaning assembly including an oscillatable septum comprises the stepof disposing a cleaning assembly including a metallic oscillatableseptum.
 44. The method of claim 43, further comprising the step ofdisposing an electromagnet near the septum for generating a magneticfield acting on the septum for bending the septum.
 45. A method ofassembling a self-cleaning printer, comprising the steps of: (a)providing a print head, the print head having a surface defining anorifice therethrough, the orifice susceptible to contaminant obstructingthe orifice; (b) disposing a cleaning assembly proximate the surface fordirecting a flow of liquid along the surface and across the orifice toclean the contaminant from the orifice, the step of disposing a cleaningassembly including the steps of: (i) providing a cup for sealinglysurrounding the orifice, the cup defining a cavity therein; (ii)disposing an elongate oscillatable septum in the cup perpendicularlyopposite the orifice for defining a gap between the orifice and theseptum, the gap sized to allow the flow of liquid through the gap, theseptum dividing the cavity into an first chamber and an second chambereach in communication with the gap, the septum accelerating the flow ofliquid to induce a hydrodynamic shearing force in the flow of liquidwhile the septum oscillates, whereby the shearing force acts against thecontaminant while the shearing force is induced in the flow of liquid,whereby the contaminant is cleaned from the orifice while the shearingforce acts against the contaminant and whereby the contaminant isentrained in the flow of liquid while the contaminant is cleaned fromthe orifice; (iii) providing a valve system to be disposed in fluidcommunication with the gap for changing flow of the fluid from the firstdirection to a second direction opposite the first direction; (iv)disposing a pump in fluid communication with the second chamber forpumping the liquid and entrained contaminant from the gap and into thesecond chamber; and (c) connecting a controller to the cleaning assemblyand the print head for controlling operation thereof.
 46. The method ofclaim 45, further comprising a pair of opposing transducers connected tothe septum for oscillating the septum.
 47. The method of claim 45further comprising the step of disposing a pressurized gas supply influid communication with the gap for injecting a pressurized gas intothe gap to form a multiplicity of gas bubbles in the flow of liquid forenhancing cleaning of the contaminant from the orifice.
 48. The methodof claim 45, further comprising the step of disposing a reciprocatingpiston in fluid communication with the first chamber for generating aplurality of pressure waves in the flow of liquid to enhance cleaning ofthe contaminant from the orifice.
 49. The method of claim 45, whereinthe step of disposing a cleaning assembly including an oscillatableseptum comprises the step of disposing a cleaning assembly including anexpandable oscillatable septum having a bore therein.
 50. The method ofclaim 49, further comprising the steps of: (a) coupling a pump to thebore for pumping a gas into the bore, so that the septum expands from afirst volume thereof to a second volume greater than the first volume assaid pump pumps the gas into the bore; and (b) coupling a bleed valve tothe bore for releasing the gas from the bore, so that the septumcontracts to the first volume as said valve releases the gas from thebore.
 51. The method of claim 45, wherein the step of disposing acleaning assembly including an oscillatable septum comprises the step ofdisposing a cleaning assembly including an oscillatable metallic septum.52. The method of claim 51, further comprising an electromagnet disposednear the septum for generating a magnetic field acting on the septum forbending the septum.
 53. The method of claim 45, further comprising thestep of disposing a closed-loop piping circuit in fluid communicationwith the gap for recycling the flow of liquid through the gap.
 54. Themethod of claim 53, wherein the step of disposing the piping circuitcomprises the steps of: (a) disposing a first piping segment in fluidcommunication with the first chamber; and (b) connecting a second pipingsegment to the first piping segment, the second piping segment in fluidcommunication with the second chamber and connected to the pump, wherebythe pump pumps the flow of liquid and entrained contaminant from thegap, into the second chamber, through the second piping segment, throughthe second piping segment, into the first chamber and back into the gap.55. The method of claim 54, further comprising the steps of: (a)connecting a first valve to the first piping segment, the first valvebeing operable to block the flow of liquid through the first pipingsegment; (b) connecting a second valve to the second piping segment, thesecond valve being operable to block the flow of liquid through thesecond piping segment; and (c) interposing a suction pump between thefirst valve and the second valve for suctioning the liquid and entrainedcontaminant from the first piping segment and the second piping segmentwhile the first valve blocks the first piping segment and while thesecond valve blocks the second piping segment.
 56. The method of claim55, further comprising the step of connecting a sump to the suction pumpfor receiving the flow of liquid and contaminant suctioned by thesuction pump.
 57. The method of claim 53, further comprising the step ofconnecting a filter to the piping circuit for filtering the contaminantfrom the flow of liquid.
 58. The method of claim 45, further comprisingthe step of connecting an elevator to the cleaning assembly forelevating the cleaning assembly into engagement with the surface of theprint head.
 59. The method of claim 58, wherein the step of connectingan elevator comprises the step of connecting an elevator is to thecontroller, so that operation of the elevator is controlled by thecontroller.